1. Field of the Invention
The present invention relates to a lithographic apparatus comprising a deformation sensor to measure the deformation of a part of the lithographic apparatus.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Undesirable deformation of components of a lithographic apparatus may jeopardize the obtainable accuracy of said lithographic apparatus. For instance, deformation of a substrate holder configured to hold a substrate will influence the position of the substrate held by the substrate holder. This effect is even worse when the substrate holder is moved with increasing accelerations in order to improve the throughput, because the deformation of the substrate holder will likewise increase due to these accelerations.
One approach to minimize the deformations is to use a very stiff and consequently heavy substrate holder. However, also in view of the desire to use larger substrates and thus larger substrate holders, this becomes impractical. As a result, the concept of a rigid body substrate holder is left in recent developments, and instead it has been proposed to accept the presence of deformations, to measure them accurately, and to compensate them by using respective actuators in the substrate holder. In such a way, the occurring deformations are actively suppressed, which increases the obtainable accuracy of the lithographic apparatus without using bulky and consequently heavy structures.
However, so far it has been a challenge to measure the deformations of a part of the lithographic apparatus with sufficient accuracy. A further drawback is that supply wires, e.g., to carry power signals and/or information signals to and from said part, introduce disturbances to the part in case the part is a moving part within the lithographic apparatus.